Myc homology region II-associated protein and uses thereof

ABSTRACT

The present invention provides a novel MHRII-associated protein designated MHRII-AP62 and antibodies immunoreactive with the MHRII-AP62 protein. Also provided are kits containing these antibodies and methods of using the antibodies for the detection of the MHRII-AP62 protein. The present invention also provides for a nucleic acid encoding the MHRII-AP62 protein and nucleic acid probes for use in the detection of the MHRII-AP62 protein. Further provided by the present invention are agents that mimic the activity of the MHRII-AP62 protein by binding to the MHRII, agents that inhibit the activity of the MHRII-AP62 protein by binding to the MHRII-AP62 protein, or by binding to the nucleic acid encoding the MHRII-AP62 protein, and methods of using these agents to treat cancer and cancer causing diseases.

RELATED APPLICATION

[0001] This application is a continuation-in-part of co-pending U.S. patent application No. 08/946,692, filed Oct. 8, 1997, now pending, the contents of which are expressly incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

[0002] This invention was made with government support under NIH Grant No. RO1 HD28317. As such, the government has certain rights in this invention.

BACKGROUND OF THE INVENTION

[0003] Members of the Myc family of nuclear proto-oncogenes (c-, N- and L-Myc) play central roles in the control of normal growth and development and in genetic pathways linked to cellular transformation and apoptotic cell death. Accumulating structural, biochemical and genetic evidence affords the view that the function of Myc family oncoproteins in these diverse processes relates in part to their roles as sequence-specific transcription factors. Myc family proteins possess a multifunctional amino-terminal domain with transactivation potential, a region rich in basic amino acid residues responsible for sequence-specific DNA-binding activity, and a carboxy-terminal alpha-helical domain required for dimerization with another bHLH/LZ protein, Max. All known biological and biochemical activities of Myc are highly dependent upon its association with Max. In addition to its key role as an obligate partner in transactivation-competent Myc/Max complexes, Max can also repress Myc-responsive genes through the formation of transcriptional-repression complexes with members of the Mad family.

[0004] Several lines of evidence support the view that Mad and Mxi1 are important tumor suppressors. First, the addition of Mad or Mxi1 can dramatically reduce the oncogenic activity of Myc/Ras in the REF cooperation assay. Second, Nisen and coworkers (Chen, J., Willingham, T., Margraf, L. R., Schreiber-Agus, N., DePinho, R. A., and Nisen, P. D., Nature Medicine 1:638-643 (1995)) have shown that adenoviral constructs encoding Mad profoundly inhibit the proliferation and tumorigenicity of established human tumor cell lines. Third, Mad and Mxi1 map to cancer hotspots that are altered in a broad spectrum of different tumor types. Lastly, the preliminary assessment of Mxi1 knockout mice indicates that Mxi1-deficiency is associated with a cancer-prone condition.

[0005] From a mechanistic standpoint, the ability of Mad and Mxi1 to act as potent anti-Myc agents is dependent upon a short amino-terminal alpha-helical domain that allows for association with a mammalian protein that is structurally homologous to the yeast transcriptional repressor SIN3. The mechanistic basis for the mouse Sin3-mediated repression appears to be mediated in part through the recruitment of: (1) NcoR, a nuclear co-repressor that directly impacts on Po1 II activity and (2) HD-1, a histone deacetylase that deacetylates histone H3 and H4 tails resulting in a condensed and less accessible nucleosomal arrangement. Structure-function studies of Sin3 indicate that its interaction with HD-1 is a critical requirement for Sin3-mediated anti-oncogenic activity in the context of Myc-induced cellular transformation.

[0006] Two domains known to be absolutely essential for Myc oncogenic activity have been mapped to the C-terminal bHLH/LZ structure and an amino-terminal segment designated Myc homology region II (MHRII). The inventors have recently cloned the drosophila homologue of Myc and have demonstrated that both of these signature features are conserved and, more strikingly, that drosophila Myc gene is oncogenic in mammalian cells. Over-expression of an MHRII fragment has been shown by others to inhibit the ability of Myc or E1a to cooperate with activated Ras in the REF assay. This finding, coupled with the formation of a specific complex between MHRII and a nuclear factor, suggests that MHRII oncogenic activity is dependent upon its ability to interact with an unidentified nuclear factor.

[0007] Myc has been shown to be directly involved in the genesis and progression of many different tumor types. Moreover, even when Myc deregulation is not the principal genetic lesion in human cancers, many cancer-associated lesions affect signaling pathways that feed into Myc and require Myc function in order to maintain the malignant phenotype.

[0008] Accordingly, there is a great need for the discovery of and characterization of proteins that interact with the MHRII of Myc. The isolation and characterization of proteins that interact with the MHRII of Myc allows for the design of agents that interact directly with MHRII to affect the regulation of Myc and ultimately target the actions of Myc. Targeting the actions of Myc oncoprotein can potentially have a significant impact on a very wide variety of human cancers, as well as many disorders arising from deregulated cellular growth or survival such as auto-immune disorders and psoriasis, among others.

SUMMARY OF THE INVENTION

[0009] The present invention provides for a novel purified Myc homology region II (MHRII)-associated protein, designated MHRII-AP62. Further provided by the present invention are antibodies immunoreactive with the MHRII-AP62 protein. Also provided are kits comprising MHRII-AP62 antibodies and methods of using the antibodies for the detection of the MHRII-AP62 protein and the diagnosis of cancers.

[0010] Further provided by the present invention is a nucleic acid sequence encoding the MHRII-AP62 protein, nucleic acid probes which hybridize to the nucleic acid sequence, and kits containing the probes for use in the diagnosis of cancers.

[0011] The present invention also provides a vector comprising a nucleic acid encoding a MHRII-AP62 protein, a cell stably transformed with this vector, as well as a method for producing recombinant MHRII-AP62 protein.

[0012] Also provided by the present invention are agents that mimic the activity of the MHRII-AP62 protein and bind to the binding domain of MHRII. Further provided are agents that inhibit the activity or expression of the MHRII-AP62 protein and inhibit the binding of the protein to MHRII, thus providing a means for assessing small molecule inhibitors to block or enhance MHRII-AP62 and MHRII interactions. Also provided are methods of treating cancer causing disease and reducing tumor growth using the agents.

[0013] Additional objects of the invention will be apparent from the description which follows.

BRIEF DESCRIPTION OF THE FIGURES

[0014]FIG. 1 sets forth results of in vitro transcription/translation experiments of MHRII-AP62 (TNT, Promega). The entire two hybrid derived cDNA produces a protein of ˜45kDa. The anti-sense construct (MHRII #62 antisense) and the empty vector (pRSCT c) were included as negative controls, while TBP (top three lanes) served as a positive control. MHRII #62 (lanes 4, 5 and 6 from the top) are from separate batches of the same reaction parameters. Molecular mass markers are shown in kilodaltons. The kDa marker sizes are as follows, starting from the top: 190, 108, 84, 67, 55, 39.5 and 35 kDa.

[0015]FIG. 2 sets forth the results of a GST pull down assay using the ³⁵S, IVT product of AP62 with GST alone and GST-MYC (a.a.1-204). TBP w/GST was used as a positive control.

[0016]FIGS. 3A and 3B set forth the results of a GST pull down assay using the ³S, IVT product of MHRII-AP62 with GST alone, GST-MYC (a.a.1-204), GST-12S E1A or GST-13S E1A. TBP was used as a positive control.

[0017]FIG. 4 sets forth the results of a zoo blot. Human, mouse, xenopus and zebra fish DNAs were probed with the entire two-hybrid derived fragment of MHRII-AP62.

[0018]FIG. 5 sets forth the results of a Northern blot using MHRII-AP62 as a probe and mouse RNAs from different embryonic developmental stages and from different tissues in adults and newborns. The single ˜5.2 kb transcript is seen, and appears to be up-regulated steadily from stages 9.5 to 15.5.

[0019]FIG. 6 shows the results of a Northern blot using MHRII-AP62 as a probe and mouse RNAs from different tissues of adult and newborn. The highest levels of expression are seen in thymus and spleen. Expression in brain and kidney correlates with Myc.

[0020]FIGS. 7A and 7B set forth the partial cDNA nucleic acid sequence (FIG. 7A), and the corresponding amino acid sequence (FIG. 7B), of the murine MHRII-AP62 protein.

[0021]FIGS. 8A and 8B set forth the complete cDNA nucleic acid sequence (FIG. 8A), and the corresponding amino acid sequence (FIG. 8B), of the murine MHRII-AP62 protein.

[0022]FIGS. 9A and 9B set forth the complete cDNA nucleic acid sequence (FIG. 9A), and the corresponding amino acid sequence (FIG. 9B), of the human MHRII-AP62 protein. The human cDNA was isolated by sequence comparison with the murine MHRII-AP62 cDNA of FIG. 8A. One of the aligned ESTs (Genebank Accession No. A1798977) was sequenced completely to obtain the sequence of FIG. 9A.

[0023]FIG. 10 is a comparison of the murine and human MHRII-AP62 nucleotide sequences.

[0024]FIG. 11 is a comparison of the murine and human MHRII-AP62 amino acid sequences.

[0025]FIG. 12 indicates the localization of the MHRII -AP62 gene on the human chromosome, 3q112-q13.1.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention provides for a novel purified Myc homology region II (MHRII)-associated protein, herein designated MHRII-AP62. As used herein, a “Myc homology region II-associated protein” is a protein that interacts with Myc homology region II to affect the oncogenic activity of MHRII. The MHRII-associated protein is preferably 40-50 kDa, and includes the human, rat and mouse analogues of the protein. Also provided by the present invention are mutated forms of the MHRII-AP62 protein. As used herein, a “mutated MHRII-AP62 protein” is the mutated form of the MHRII-AP62 protein, wherein the nucleic acid encoding the mutated MHRII-AP62 protein contains one or more deletion, insertion, point or rearrangement mutations, or a combination thereof, that may render the protein encoded by the nucleic acid nonfunctional or inactivated. The MHRII-AP62 protein of the present invention may be produced synthetically or recombinantly, or may be isolated from native cells.

[0027] The present invention also provides antibodies immunoreactive with the MHRII-AP62 protein. The antibodies may be polyclonal or monoclonal, and are produced by standard techniques known to one skilled in the art. The antibodies of the present invention may be employed without further change, or may be reduced to various sized fragments. The antibodies described herein may be labeled with cytotoxic agents, antibiotics, and standard detectable markers, such as chemiluminescent detection systems, radioactive labels such as ¹²⁵I, and enzymes such as horseradish peroxidase, biotin, and avidin.

[0028] The antibodies provided by the present invention may be presented in kits with detectable labels and other reagents and buffers for such detection. For example, an antibody may be presented as part of a serological reagent for identification of an MHRII-AP62 protein. The labeled antibodies presented in the kits may be labeled with any standard detectable markers, such as chemiluminescent detection systems, radioactive labels such as ¹²⁵I, and enzymes such as horseradish peroxidase, biotin, and avidin.

[0029] The present invention further provides a method of detecting the presence of an MHRII-associated protein in a biological sample comprising contacting the sample with an antibody immunoreactive with the MHRII-AP62 protein and detecting the antibody bound to the protein. The MHRII-associated protein may be detected in biological samples such as body fluids and cell culture. The presence of and the level of the MHRII-associated protein may be determined using the antibody immunoreactive with MHRII-AP62 protein by procedures known in the art including, but not limited to, immunoblotting, immunoprecipitation, solid phase radioimmunoassay (e.g. competition RIAs, immobilized antigen or antibody RIAs, or double antibody RIAs), enzyme-linked immunoabsorbant assay, and the like. In one embodiment of the invention, the antibody immunoreactive with the MHRII-AP62 protein may be used to determine the location of the MHRII-AP62 protein in a cell.

[0030] The present invention provides a purified and isolated nucleic acid encoding a MHRII-AP62 protein. As used herein, the nucleic acid may be genomic DNA, cDNA, RNA or antisense RNA and includes nucleic acid derived from any species, e.g., human, rat, and mouse. Due to the degeneracy of the genetic code, the nucleic acid of the present invention also includes a multitude of nucleic acid substitutions which will encode MHRII-AP62. The nucleic acid from the mouse preferably encodes the amino acid sequence for MHRII-AP62 as shown in FIG. 7B, and more preferably comprises the nucleotide sequence as shown in FIG. 7A. Even more preferably, the nucleic acid from the mouse encodes the amino acid sequence for MHRII-AP62 as shown in FIG. 8B, and more preferably comprises the nucleotide sequence as shown in FIG. 8A. The nucleic acid from the human preferably encodes the amino acid sequence for MHRII-AP62 as shown in FIG. 9B, and more preferably comprises the nucleotide sequence as shown in FIG. 9A. The present invention also includes nucleic acid sequences that are at least 80%, preferably at least 85%, more preferably at least 90%, and most preferably at least 95%, homologous with each of the nucleic acid sequences set forth above.

[0031] In order to determine the full length nucleic acid sequence encoding the MHRII-AP62 protein, oligonucleotide probes designed from the partial cDNA sequence encoding the MHRII-AP62 protein, which are described herein, may be used to isolate a full length cDNA from a cDNA library. The mouse cDNA sequences may be used as probes for screening a human cDNA library in order to obtain the sequence encoding the human homologue of the protein. The oligonucleotide probes may be obtained from a commercial source (Genset, Genelink, Perkin-Elmer, or other sources), and may be labeled with ³²P using methods commonly known to those skilled in the art. The cDNA libraries may be obtained from a commercial source (Clontech) and are plated onto an appropriate membrane (nitrocellulose or Nytran, Scheicher and Schuell; Genescreen, DuPont/NEN). The cDNA libraries may be, for example, human, rat or mouse cDNA libraries. The membrane is hybridized with the labeled oligonucleotide probe, the unbound probe is removed by washing, and then the cDNA hybridizing with the oligonucleotide is detected using an appropriate method, many of which are known to one skilled in the art. The bacterial colony or bacteriophage plaque corresponding to the cDNA on the membrane is recovered, amplified, and rescreened as described above, until a single colony or plaque that hybridizes to the oligonucleotide is obtained.

[0032] The full length nucleotide sequence encoding MHRII-AP62 may also be obtained using the two-hybrid method as described in Vojtek, et al. (1993) Cell 74:205-214.

[0033] The cDNA clone, obtained using any of the methods described above, is then sequenced using the standard dideoxynucleotide method, known to one of skill in the art. The amino acid sequence may then be deduced from the nucleotide sequence, based upon the genetic code.

[0034] Alternatively, the full length nucleic acid sequence encoding the MHRII-AP62 protein is determined by deducing the nucleic acid sequence from the amino acid sequence, preparing an oligonucleotide, and screening a cDNA library. The protein is first isolated by isolation and purification methods such as high performance liquid chromatography (HPLC) with reverse phase columns, ion exchange columns, and gel filtration columns. Methods by which the MHRII-AP62 protein may be sequenced are known to one of skill in the art and include methods such as the Edman degradation procedure and various mass spectrophotometer procedures.

[0035] The nucleic acid sequence encoding the MHRII-AP62 protein can be prepared several ways. For example, it can be prepared by isolating the nucleic acid sequence from a natural source, or by synthesis using recombinant DNA techniques. In addition, mutated nucleic acid sequences encoding the MHRII-AP62 protein can be prepared using site mutagenesis techniques. The amino acid sequences encoded by the MHRII-AP62 nucleic acid sequence may also be synthesized by methods commonly known to one skilled in the art (Modern Techniques of Peptide and Amino Acid Analysis, John Wiley & Sons (1981); M. Bodansky, Principles of Peptide Synthesis, Springer Verlag (1984)). Examples of methods that may be employed in the synthesis of the amino acid sequences, and mutants of these sequences include, but are not limited to, solid phase peptide synthesis, solution method peptide synthesis, and synthesis using any of the commercially available peptide synthesizers. The amino acid sequences, and mutants thereof, may contain coupling agents and protecting groups used in the synthesis of the protein sequences, and are well known to one of skill in the art.

[0036] The present invention also provides a vector comprising a nucleic acid encoding a MHRII-AP62 protein, as well as a cell stably transformed with the vector. The vector may be any plasmid, viral-derived nucleic acid, lytic bacteriophage derived from phage lambda, cosmid, filamentous single-stranded bacteriophage such as M13, and the like, for cloning the MHRII-AP62 nucleic acid or introducing the nucleic acid into a cell for expression. The cell may be eukaryotic or prokaryotic. Suitable host cells include, but are not limited to, bacterial cells such as E. coli, Bacillus subtilis, Agrobacterium tumefaciens, Bacillus megaterium, eukaryotic cells such as Pichia pastoris, Chlamydomonas reinhardtii, Cryptococcus neoformans, Neurospora crassa, Podospora anserina, Saccharomyces cerevisiae, Saccharomyces pombe, Uncinula necator, cultured insect cells, cultured chicken fibroblasts, cultured hamster cells, cultured human cells such as HT1080, MCF7, 143B and cultured mouse cells such as EL4 and NIH3T3 cells. Such expression systems may be used to produce a MHRII-AP62 protein by culturing a cell transformed with a vector comprising a nucleic acid encoding the MHRII-AP62 protein, and recovering recombinant MHRII-AP62 protein from the culture.

[0037] The present invention also provides single-stranded nucleic acid probes and mixtures thereof for use in detecting the presence of a nucleic acid encoding the MHRII-AP62 protein. The nucleic acid probes may be DNA, cDNA, or RNA, and are prepared from the nucleic acid sequence encoding the MHRII-AP62 protein. The probes may be the full length sequence, or fragments thereof. Typical probes are 12 to 40 nucleotides in length. Generally, the probes are complementary to the gene coding sequences, although probes to introns are also contemplated. The probes may be synthesized using an oligonucleotide synthesizer, and may be labeled with a detectable marker such as fluorescence, enzyme or radiolabeled markers including ³²P and biotin, and the like. Combinations of two or more labeled probes corresponding to different regions of the nucleic acid sequence also may be included in kits to allow for the detection and/or analysis of the nucleotide sequence encoding the MHRII-AP62 protein.

[0038] The present invention further provides agents that prohibit the MHRII-AP62 protein from binding to MHRII. The agents may inhibit the binding of the MHRII-AP62 protein to the MHRII binding domain by mimicking the binding capabilities of the MHRII-AP62 protein, thereby preventing the binding of the MHRII-AP62 protein to MHRII. The agent, when bound to the MHRII binding domain, directly affects the deregulation of Myc, thereby affecting the occurrence and progression of many different types of cancers and benign proliferation disorders characterized by an abnormal proliferation of cells. Even where Myc deregulation is not the principle genetic lesion in the cancer, many cancer-associated lesions affecting signal pathways that feed into Myc and require Myc function in order to maintain the malignant phenotype. Thus, targeting the actions of Myc oncoprotein by preventing the binding of Myc-associated proteins to the Myc homology region II can potentially have a significant impact on a wide variety of human cancers. In one embodiment of the invention, the physical structure of the MHRII-AP62 protein complexed with MHRII is analyzed and agents which mimic the binding action of the MHRII-AP62 protein are designed based on this physical structure.

[0039] Also provided by the present invention are agents which inhibit the activity of the MHRII-AP62 protein by directly binding to the MHRII-AP62 protein itself. These agents prevent the MHRII-AP62 protein from binding to MHRII, thus inhibiting Myc-mediated malignant transformation. Agents that bind to the MHRII-AP62 protein may be stereochemically designed so that, based upon the structure of the MHRII-AP62 protein, they will bind to the protein and inhibit activity.

[0040] Alternatively, the agents provided by the present invention may be nucleic acid sequences or proteins that directly bind to the amino acid sequence or the nucleic acid sequence of the MHRII-AP62 protein and thereby affect transcription or translation of the sequence, ultimately inhibiting or altering the activity of the MHRII-AP62 protein and its ability to bind to MHRII.

[0041] The agents of the present invention may comprise proteins, polypeptides, peptides, nucleic acid sequences, small non-peptide organic molecules and organic reagents. The nucleic acid sequences may comprise, for example, RNA, antisense RNA, double stranded RNA, RNA-DNA hybrids, double stranded DNA, nucleotides, oligonucleotides, or antisense oligonucleotides. The antisense nucleic acid sequences are engineered to act on the mRNA of the nucleic acid sequence encoding the MHRII-AP62 protein, preventing the nucleic acid sequence from being translated into the MHRII-AP62 protein.

[0042] Further provided by the present invention is a method of treating cancer by preventing the occurrence of and inhibiting the progression of many different types of cancers and benign proliferation disorders by administering to a subject an effective amount of the agents described herein to treat the cancer. Non-limiting examples of cancers that can be treated using the agents provided by the present invention include Burkitt's lymphoma, neuroblastoma, osteosarcoma, ovarian cancer, breast cancer, leukemia, lung cancer, colorectal cancer and prostate cancer. Non-limiting types of benign proliferation disorders that are characterized by an abnormal proliferation of cells include autoimmune diseases such as lupus, rheumatoid arthritis and psoriasis.

[0043] The present invention is described in the following Experimental Details Section, which is set forth to aid in an understanding of the invention, and should not be construed to limit in any way the invention as defined in the claims which follow thereafter.

[0044] Experimental Details Section

[0045] Derivation of the Two-Hybrid MHRII-AP62 cDNA. To identify proteins that associate with MHRII, a modified version of the yeast two-hybrid screen method (Vojtek, et al. (1993) Cell 74:205-214; Schreiber-Agus, et al. (1995) Cell 80:777-786) developed by Fields and Song (Nature 340:245-246 (1989)) was employed. Standard manipulations of yeast were performed essentially as described in Schreiber-Agus, et al. (1995) Cell 80:777-786. A non-transactivating MHRII bait was constructed for use in the yeast two-hybrid screen. A HeLa cDNA activator library yielded several candidate clones. A partial cDNA of one of these MHRII interacting clones designated MHRII-AP62 was analyzed.

[0046] Preparation of the MHRII bait (fusion plasmid). PCR (polymerase chain reaction) was performed on the mouse c-myc gene using the following oligonucleotides: ˜PG1: 5′ TgA TgA CCg AAT TCC TTg gAg gAg 3′ ˜RD335: 5′ CCA gCT Tgg Cag Cgg CTg Ag 3′

[0047] An EcoRI site was created at the 5′ end and a PstI site at the 3′ end. The fragment was subcloned into the pBTM116 vector (from P. Barte and S. Fields, SUNY Stony Brook) and introduced into the yeast strain S. cerevisiae L40 (from S. Hollenberg, Seattle, Wash.). The fusion plasmid produces a fusion protein consisting of amino acid #104 (E) to amino acid #140 (A) of c-Myc fused to the LexA DNA binding domain. A mouse T cell lymphoma cDNA library in the pACT vector (Clontech) (generates fusion to the transactivation domain) was introduced into the L40 yeast strain expressing the MHRII bait.

[0048] In vitro Transcription/Translation Experiments of MHRII-AP62. The in vitro transcription/translation experiments of MHRII-AP62 (TNT, Promega) were performed. (See FIG. 1) The entire two hybrid derived cDNA produces a protein of ˜45kDa. The anti-sense construct and the empty vector were included as negative controls, while TBP served as a positive control. MR #62 1, 2, and 3 are from separate batches of the same reaction parameters.

[0049] The in vitro transcription/translation reactions were performed using a TNT kit (Promega)as stated below: TNT rabbit reticulocyte lysate 25 μl  TNT reaction buffer 2 μl T7 RNA polymerase 1 μl Amino acid mixture minus methionine, 1 mM 1 μl ³⁵S-methionine (1,000 Cl/mmol) at 10 mCl/ml) 4 μl Rnasin ribonuclease inhibitor (40 u/μl) 1 μl DNA substrate Nuclease-free H₂O to final volume 50 μl  1 μg pGEM-37-TBP: reaction performed for 60 min. (3 tubes) 0.5 μl pRSET-AP62 reaction performed for 90 min. (3 tubes) 1 μg pRSET_(c) reaction performed for 90 min. (1 tube) 1 μg pRSET_(c):AP62 reaction performed for 90 min. (1 tube) (antisense) (from miniprep)

[0050] 2 μl of each reaction was removed and added 2 μl of 2× SDS loading buffer and boiled for 5 min. and analyzed on a 15% SDS-PAGE. The remainder was frozen in dry ice and stored at −70° C.

[0051] GST Pull Down Assays. GST pull down assays were performed using the 35S, IVT product of AP62 with GST alone, GST-MYC (a.a.1-204), GST-12S E1A or GST-13S E1A. (See FIGS. 2 and 3) AP62 clearly associates with both E1As and MYC, but not GST. 0.5 M NaCl was used in these washes, so the AP62-MYC in vitro interaction is a very strong one. TBP was used as a positive control for binding to GST-MYC and was generated by in vitro transcription/translation as well.

[0052] Zoo Blot. Human, mouse, xenopus and zebra fish DNAs were probed with the entire two-hybrid derived fragment of AP62. The results are presented in FIG. 4, and show that the mouse AP62 probe readily cross hybridizes with sequences in the human genome under low-stringency conditions only.

[0053] Northern Blots. Northern blots were performed using AP62 as a probe and mouse RNAs from different embryonic developmental stages and from different tissues in adults and newborns as described in Sambrook, et al. (1989) Molecular Cloning: A Laboratory Manual. CSH Laboratory; Cold Spring Harbor. The results are shown in FIGS. 5 and 6. The single ˜5.2 kb mRNA transcript of the MHRII-AP62 protein is seen, and appears to be up-regulated steadily from stages 9.5 to 15.5. The highest levels of expression are seen in thymus and spleen. The expression of MHRII-AP62 in brain and kidney correlates with Myc expression.

[0054] Analysis of partial cDNA clone. The partial sequence for the cDNA of MHRII-AP62 and its corresponding deduced amino acid sequence were determined and are shown in FIGS. 7A and 7B. The analysis of the partial cDNA of the MHRII-AP62 clone revealed: (1) no sequence homology to any protein in eukaryotic genome databases, (2) direct interaction between MHRII or E1a and MHRII-AP62 in GST pull-down assays, and (3) broad tissue distribution of MHRII-AP62 mRNA.

[0055] Isolation and Analysis of full cDNA clone. A cDNA 5′ probe was generated from the partial mouse cDNA of FIG. 7A and was used to isolate a full length cDNA from a mouse 11d embryo 5′ stretch cDNA library (Clontech). The sequence for the isolated cDNA of MHRII-AP62 and its corresponding deduced amino acid sequence were determined and are shown in FIGS. 8A and 8B.

[0056] Isolation and Analysis of Human cDNA clone. The human cDNA clone was isolated by sequence comparison of the mouse MHRII-AP62 sequence with the database. A number of different human EST clones aligned with the murine sequence. One of the EST clones (GeneBank Accession No. A1798977) was obtained and fully sequenced. The full sequence and its corresponding deduced amino acid sequence are shown in FIGS. 9A and 9B.

[0057] All publications mentioned hereinabove are hereby incorporated by reference in their entirety.

[0058] While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by one skilled in the art from a reading of the disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims. 

What is claimed is:
 1. A purified and isolated nucleic acid encoding a MHRII-associated protein (MHRII-AP62).
 2. The nucleic acid of claim 1 that is derived from a human or a mouse.
 3. The nucleic acid of claim 2 that is derived from a human.
 4. The nucleic acid of claim 3 which encodes the amino acid sequence for MHRII-AP62 as shown in FIG. 9B.
 5. The nucleic acid of claim 4, having the nucleotide sequence for MHRII-AP62 as shown in FIG. 9A.
 6. The nucleic acid of claim 2 that is derived from a mouse.
 7. The nucleic acid of claim 6 which encodes the amino acid sequence for MHRII-AP62 as shown in FIG. 8B.
 8. The nucleic acid of claim 7, having the nucleotide sequence for MHRII-AP62 as shown in FIG. 8A.
 9. A purified MHRII-associated protein (MHRII-AP62).
 10. The protein of claim 9 having a molecular weight of about 40- 